One of the functions required for a wide area network (WAN) is operations, administration and maintenance: (OAM) function. The OAM function is specified in ITU-T recommendation Y.1731, for example. In Y.1731, a LinkTrace (LT) function, which corresponds to a Traceroute function as an OAM function on the Internet, is specified. The LT function is used to obtain routing information from a node of a network.
FIG. 1 shows how a node 10 uses the LT function to acquire routing information from the local node 10 to a node 14. The node 10 sets the node 14 as a target node and transmits an LT-Request frame (referred to as “LT-RQ,” hereinafter) in which a TTL (Time To Live) value is stored. Relay nodes 11, 12 and 13 each subtract “1” from the TTL value before transferring the received LT-RQ; and set the TTL value which is obtained by the subtraction, into an LT-Reply frame (referred to as “LT-RP,” hereinafter) and transmit the LT-RP back to the node 10. The node 10 generates routing information to the node 14 on the basis of the TTL value of the LT-RP from each of the nodes 11, 12 and 13. In the example illustrated in the diagram, the TTL values are arranged in descending order. As a result, what is formed is one route that leads from the node 10 to the node 11, from the node 11 to the node 12, from the node 12 to the node 13, and from the node 13 to the node 14 (Node 10→Node 11→Node 12→Node 13→Node 14).
The use of the above LT function makes it possible to identify a location of failure on the route. FIG. 2 shows how a failure occurs in the node 13 on the network shown in the above FIG. 1. In this case, in response to an LT-RQ issued by the node 10, LT-RPs are returned from the nodes 11 and 12. However, no reply is obtained from the node 13 and subsequent nodes in response to the LT-RQ issued by the node 10. As a result, the node 10 recognizes, on the basis of the routing information, that a failure has occurred in the node 13.
By the way, when one node of the network is congested with data, the node could possibly become a performance bottleneck of the network. That is, the node that congestion occurs could be a cause of transmission delay on the route that includes the node. As for congestion of anode, for example, what is disclosed in PTL 1 is a technique for regulating a call originating from a subscriber to a node when congestion occurs in the node.